The invention relates to conveyor belts having electrical conductors, which are sensor loops embedded therein, and more particularly to belts having signal inverting type sensor loops.
It is known to transport bulk materials, such as metallic ore and the like, with a heavy duty conveyor belt. These belts may be on the order of miles (1 mile=1.6 kilometers) long. Sharp edges of the material being transported may become lodged in such a position in the conveyor belt mechanism that they can cause a rip (slit, cut or tear) in the belt. When such a rip or tear commences, if the belt is not stopped, the rip can propagate longitudinally for a substantial distance along the belt. Ripped or torn portions of the belt must then be repaired. The costs can be quite formidable for repairing such heavy duty conveyor belts, as well as the cost of cleaning up material which has spilled off of the conveyor belt. It is therefore generally well known to detect and locate a rip in the belt as quickly as possible after it commences, thereby minimizing the extent of the damage to the belt.
It is therefore known to employ sensors within the conveyor belts as part of a rip detection system. These sensors may take the form of loops of conductive wire, and operate in conjunction with an overall rip detection system. Generally, the rip detection system functions by xe2x80x98inferentiallyxe2x80x99 determining whether a sensor (sensor loop) has been damaged, i.e., is an open circuit rather than a closed circuit, as a result of a rip or tear in the belt. Typically an electrical energy source external to the belt is inductively or capacitively coupled to a sensor in the belt. For example, a transmitter/receiver (exciter/detector) external to the belt and which is inductively or capacitively coupled to the sensor is used to detect a break in the conductive wire loop of the sensor. A plurality of such sensors may be disposed at a corresponding plurality of intervals along the length of the conveyor belt. Also, a plurality of exciter/detectors may be disposed at various locations adjacent the length of the belt. In this manner, the damage from rips or tears can be minimized.
U.S. Pat. No. 3,742,477 (Enabnit; 1973) discloses a conveyor belt condition monitoring apparatus for monitoring the open-circuited or close-circuited condition of electrical conductors associated with the conveyor belt. The electrical conductors comprise sensor loops, and are embedded in the conveyor belt. Generally, the monitoring apparatus comprises a detector circuit including an oscillator disposed so as to detect the proximate passage of a close-circuited (i.e., undamaged) sensor loop. The sensor loops disclosed in this patent each employ a single wire which passes (crosses) over (or under) itself in at least two places in order to form a pair of inverted coils. As a general proposition, an elongate element (e.g., a conductor), which is used to form a pair of inverted coils can be described as a xe2x80x9cfigure-eight sensor loopxe2x80x9d will have at least one xe2x80x9ccrossoverxe2x80x9d.
U.S. Pat. No. 4,621,727 (Strader; 1986) discloses a conveyor belt damage sensor in which conductors freely move during flexing of the belt by enclosing the conductors in low coefficient of friction jacketing envelopes. As illustrated in FIG. 5 of this patent, a (sensor) conductor is disclosed which comprises a coiled conductor (62) surrounded by an extruded thermoplastic resin envelope (60). Multiple formations of figure-eight sensor loops are disclosed wherein the conductor contained within its envelope passes (crosses) over/under itself multiple times.
U.S. Pat. No. 4,854,446 (Strader; 1989;xe2x80x9c""446 Patentxe2x80x9d) discloses electrical conductors formed into a xe2x80x9cfigure-eightxe2x80x9d pattern embedded in a conveyor belt. The electrical conductors of the sensor loops may be xe2x80x9cwavyxe2x80x9d, in the form of a repeating flat sinusoidal wave form, to accommodate flexure of the belt without losing continuity (close-circuitness). A typical conveyor belt construction is shown in FIG. 6 of the patent. The belt (90) has a top layer (92) which has an outer load carrying surface or xe2x80x9ccoverxe2x80x9d, and a bottom layer (94) which has an outer pulley engaging surface or cover. The bottom layer is sometimes referred to as a xe2x80x9cpulley coverxe2x80x9d. Reinforcing cables (98) are disposed between the top and bottom layers. Each of the top and bottom layers has a layer (100) of insulation gum on an inner surface thereof, for engaging with each other and with the cables (98). The electrical conductors (sensor loops) (108) are shown as being disposed between the bottom layer (94) and the cables (98), with an insulation layer (104) and an optional fabric layer (106) lying between the conductors (108) and the cables (98).
FIG. 1, comparable to FIG. 1 of the ""446 patent, illustrates the prior art rip detection system as set forth in the ""446 patent to Strader. A belt rip detection system is shown generally by reference numeral 100. An elastomeric conveyor belt 104 is driven around/over rollers or pulleys 102 and 103. A motor 110 provides the power to drive roller 103 which in turn drives the conveyor belt 104 in a direction of travel as indicated by arrow 111. Of course, the motor could also drive the belt in the opposite direction.
A plurality of conductors 105 (sensor loops or sensors) are embedded in the elastomeric belt 104 transverse to the direction of travel. The conductors 105 are arranged generally in a signal inverting format.
The conductors/sensors 105 may be used in connection with a rip detection system which may use either magnetic or electric fields for excitation/detection. The conductors 105 carry a current flow therein when subjected to an electrical or magnetic field. A rip in the belt 104 will eventually propagate far enough to cause one of the conductors 105 to be broken. A transmitter 106 emits an electrical or magnetic field which is communicated by conductors 105 to a receiver 107 provided that the conductor 105 is intact. Receiver 107 provides a signal to control circuitry 101 which can process the signal and indicate a rip. The rip signal may result in an alarm and/or a signal 108 to the motor controller 109 to automatically stop motor 110 and shut down the conveyor belt 104.
The electrical conductors 105 are embedded within a conveyor belt 104 which comprises an elastomeric body having a load carrying surface (cover) and a parallel pulley engaging cover with a reinforcement ply disposed within the elastomeric body. The electrical conductors 105 can be embedded into either the load carrying or the pulley engaging surfaces, located between reinforcing plies, or between a reinforcing ply and either load carrying or pulley engaging surface. The electrical conductors can be located either longitudinally or transversely with respect to the belt. The electrical conductors are arranged in a pattern such as a loop, oval, polygon, or in substantially a figure-eight.
FIG. 2, comparable to FIG. 6 in the ""446 patent, illustrates the installation of a conductor in the prior art belt construction. Reference numeral 200 denotes a conveyor belt. Load bearing surface 202 is secured to reinforcing cables 204 by gum 203. Conductor assembly 205 is comprised of insulation 206, fabric 207 and wire 208. Tie gum 209 secures the conductor assembly 205 to the cables 204 and to a bottom pulley cover 210. Compactor 201 compresses the assembly together prior to the belt being fed to a press and finally vulcanized.
FIG. 3 illustrates the crossover of the insulated coated fabric and wire of the conductor caused by forming the figure eight sensor loop configuration as disclosed in the ""446 patent. The total thickness of the crossover of insulated fabric 207 and wire portions 301 and 302 of a sensor loop 105 conductor assembly 205 is represented by reference numeral 303 and is twice the diameter of the wire plus the thickness of the fabric.
Although details of the conductor crossovers are not discussed in the prior art patents hereinabove, it should be apparent to those skilled in the art that the disclosed rip detection systems (e.g., 100) having sensor loops incorporating crossovers will not function properly unless the conductors (e.g., 105, 301, 302) are insulated or otherwise prevented from touching themselves (short-circuiting) wherever they cross over. In other words, a portion 301 of a sensor loop 105 must not be allowed to touch an other portion 302 of the same sensor loop 105.
It is desirable to minimize the thickness of conveyor belt sensors, while at the same time preventing short circuiting at sensor conductor crossovers, and also providing sensor conductors which will resist breakage due to flexure.
This invention concerns the use of microcoil springwire for conductors utilized for sensors in conveyor belt rip detection systems in order to achieve the objectives of minimizing the thickness of conveyor belt sensors, while at the same time preventing short circuiting at sensor conductor crossovers, and also providing sensor conductors which will resist breakage due to flexure.
According to the invention, a rip detection sensor for incorporation within a conveyor belt comprises a conductor formed in an endless loop arranged in a signal inverting configuration wherein the conductor crosses itself in at least one crossing place. The conductor is formed as microcoil springwire. The conductor crosses itself by crossing through itself such that the microcoil springwire resides substantially in a single plane throughout the sensor including the crossing places, and means are provided to prevent short-circuiting of the conductor at the crossing places.
According to the invention, the conveyor belt is characterized in that the short-circuit prevention means comprise insulation coating the conductor, or comprise adhesive applied between the microcoil conductor portions where they cross-through each other.
According to the invention, the conveyor belt is characterized in that the short-circuit prevention means comprise a tee having two grooves in which an elongated portion of the microcoil springwire conductor can reside to form a cross-through for the conductor, wherein the grooves are on opposite faces of the tee and are oriented substantially orthogonally to each other.
According to the invention, the conveyor belt is characterized in that the short-circuit prevention means comprise a tee having a first, second, third, and fourth cylindrical dowel, wherein the first and third dowels are on opposed sides of the tee, and the second and fourth dowels are on opposed sides of the tee; such that a first crossing portion of the microcoil springwire conductor can be wrapped around the first dowel, elongated to traverse a first side of the tee, and then wrapped around the opposing third dowel; and such that a second crossing portion of the microcoil springwire conductor can be wrapped around the second dowel, elongated to traverse a second side of the tee, and then wrapped around the opposing fourth dowel. The microcoil springwire conductor can be affixed to the tee with an adhesive.
According to the invention, the conveyor belt is characterized in that the microcoil springwire conductor comprises plated or coated high-tensile strength steel. Furthermore, the microcoil springwire comprises a coiled conductor with a pitch of between one to four conductor diameters, and a coil diameter of between 0.025 to 0.175 inches and preferably between 0.050 to 0.10 inches.
According to the invention, the conveyor belt comprises a top load bearing surface, a middle carcass layer, and a pulley cover, characterized in that the sensor is embedded within any of the three layers.
According to the invention, the conveyor belt is characterized in that the sensor includes loops configured for use in connection with a belt rip detection system which includes external transmitter/exciters, and receiver/detectors.
An aspect of the invention is a method of manufacturing a conveyor belt incorporating within it a rip detection sensor comprising a conductor formed in an endless loop arranged in a substantially figure-eight configuration wherein the conductor crosses itself in at least one crossing place, characterized by: forming the conductor as a microcoiled springwire; forming the crossing places such that the microcoil springwire conductor crosses through itself and resides substantially in a single plane throughout the sensor including the crossing places; and preventing short-circuiting of the conductor at the crossing places.
According to the invention, the method is characterized by insulating the conductor to prevent short-circuiting, or by providing adhesive between the conductor portions at the crossing places.
According to the invention, the method may be characterized by providing tees at the crossing places. The method further includes elongating portions of the conductor in the crossing places, wrapping the elongated portions of the conductor around the tees, and possibly affixing the conductor to the tees with adhesive.
A further aspect of the invention is a conveyor belt rip detection system, comprising a conveyor belt incorporating within it a rip detection sensor comprising a conductor formed in an endless loop arranged in a signal inverting configuration wherein the conductor crosses itself in at least one crossing place, and the sensor has loops. The system further comprises a drive motor, a driven roller driven by the drive motor, a following roller, an external transmitter and receiver coupled with the sensor loops, and control circuitry controllably connected between the external receiver and a motor controller for controlling the action of the drive motor. The conveyor belt rip detection system is characterized in that the conductor is formed as microcoil springwire; the conductor crosses itself by crossing through itself such that the microcoil springwire resides substantially in a single plane throughout the sensor including the crossing places; and means are provided to prevent short-circuiting of the conductor at the crossing places.
According to the invention, the conveyor belt rip detection system is characterized in that the means to prevent short circuiting is selected from the group consisting of adhesive, insulation coating the conductor, a tee having two grooves, and a tee having a first, second, third, and fourth cylindrical dowel or other non-conductive material positioned to prevent the two or more sections of microcoil from contacting each other.
Additional objects of the invention will be understood when reference is made to the Brief Description of the Drawings, Description of the Invention and Claims which follow hereinbelow.